Two U.S. soldiers died in a landmine blast by suspected al-Qaida-linked militants in the southern Philippines, in what is believed to be the second time American counterterrorism troops have been killed in the country.

A military spokesman said the soldiers were on their way to a township in Jolo Island to help build schools and dig wells, The Associated Press reported.

While the spokesman did not identify any suspects, a senior Philippine military commander told the AP that terror-group Abu Sayyaf was likely behind the landmine attack.

About 600 U.S. troops are currently stationed in the Philippines to help the country’s military fight an estimated 400 Abu Sayyaf fighters.